xliv 



General Results of the Makerstoun Observations. 



Sd, The mean difference, independent of sign, has the following epochs of maximum and minimum. 



Maximum, 

 Minimum, 

 Maximum, 

 Minimum, 



Nov. Dec. Jan. 



+ 8^ P.M. 



- Gil^ A.M. 



10>^ A.M. 



3" P.M. 



Feb. March, April. 

 + 2^^ A.M. 

 — 6^^ A.M. to 61^ P.M. 



May, .Tune, July. 

 + 2^ P.M. 

 -9^ P.M. 



Aug. .Sept. Oct. 

 ll'^P.M. 



ilh 



A.M. 



10^ A.M. 

 6*' P.M. 



77. The opposition in the epochs of maximum and minimum is even more considerable for the mean dif- 

 ference than for its positive and negative elements. We find, as has already been found for the magnetic 

 declination. No. 45, that the diurnal law of disturbance of the horizontal component varies with season, and 

 that the law for summer is nearly the reverse of that for winter. In summer, the minimum disturbance occurs 

 about 8^ P.M., which is the hour of the maximum disturbance in winter ; in summer, the maximum disturbance 

 occurs about 3"^ p.m., which is the hour of a minimum in winter, which diifers little in value from the principal 

 minimum ; the law for autumn also differs considerably from that for spring, the least values of the disturbance 

 occur in the latter between 6^ a.m and 6"^ p.m., while the greatest values occur in the former between 8^ a.m. 

 and 4'' p.m. 



78. Probable Error of Observations of the Horizontal Component. — At Makerstoun, in years of moderate 

 distui'bance, the probable error of an observation of the horizontal component from the monthly mean for the 

 hour of observation has its least values as follow : — 



Winter, between 4'^ a.m. and 4'* p.m., the probable error being less than 00004 of the whole component. 



Spring, ei^A.M. ... e'^P.M 00005 



Summer, SI^p-m. ... 8'> a.m 0-0003. 



Autumn, S'' and 4'^ a.m. and e'' p.m 0-0004 



Variation of the Horizontal Component with reference to the Moon^s Hour-Angle. — The following Table 

 has been formed from Table XXXI., 1844, p. 391, and Table XXVI., p. 15, of the present volume. 



Table 37. — Variations of the Horizontal Component of Magnetic Force with reference to the Moon's 

 Hour- Angle for the Winter and Summer Lunations, and for all the Lunations of the Years 1844 

 and 1845. 



Moon 's 



Winter Lunations. 



Summer Lunations. 



All the Lunations. 



Hour 

 Angle. 





















1844. 



1845. 



Mean. 



1844. 



1845. 



Mean. 



1844. 



1845. 



Mean. 



h. m. 



ooo 



0-00 



0-00 



0-00 



0-00 



0-no 



0-00 



0-00 



0-00 







-0066 



-0018 



-0042 



+ 0029 



+ 0050 



+ 0039 



-0019 



+ 0014 



-0002 



2 25 



-0132 



+ 0131 



0000 



+ 0021 



+ 0163 



+ 0091 



-0056 



+ 0147 



+ 0045 



4 20 



-0059 



-0107 



-0083 



+ 0018 



+ 0081 



+ 0049 



-0021 



-0019 



-0020 



6 15 



-0046 



-0046 



-0046 



-0028 



-0004 



-0016 



-0037 



-0026 



-0031 



8 10 



+ 0004 



-0112 



-0054 



-0060 



-0182 



-0121 



-0028 



-0143 



-0085 



10 5 



-0036 



-0021 j 



-0028 



-0012 



+ 0029 



+ 0008 



-0023 



+ 0003 



-0010 



12 



+ 0122 



+ 0029 



+ 0075 



+ 0086 



+ 0102 



+ 0093 



+ 0104 



+ 0063 



+ 0083 



13 55 



+ 0099 



+ 0074 ! 



+ 0086 



+ 0157 



+ 0092 



+ 0124 



+ 0128 



+ 0083 



+ 010? 



15 50 



-0001 



+ 0123 



+ 0061 



+ 0030 



-0039 



-0005 



+ 0014 



+ 0049 1 



+ 0031 



17 45 



+ 0093 



+ 0047 



+ 0070 



-0053 



-0102 



-0078 



+ 0014 



-0021 ' 



-0003 



19 40 



+ 0065 



-0025 



+ 0020 



-0126 



-0130 



-0128 



-0031 



-0073 



-0052 



21 35 



-0028 



-0081 



-0054 



-0056 



-0055 



-0056 



-0044 



-0068 



-0056 



79. The following are the conclusions from Table 37. 



There are four independent results in this Table, two for the winter lunations of 1844 and 1845, and two 

 for the summer lunations of the same years ; the other columns are derived from these : of the four results 

 three give the same law so nearly, that the result for the two years may be derived from either with but little 

 error in epochs ; that result from the last column of the Table is as follows : — 



A maximum of the horizontal component about 1^ hours after the inferior transit. 



A minimum 3 hours before the superior transit. 



A maximum 2 hours after the superior transit. 



A minimum 8 hours after the superior transit. 



